This invention relates to a coupling for use between an above-water platform or the like which is spaced above the surface of the water and a foundation which is anchored in or on the sea bottom.
There are at least two types of above-water platforms as used primarily in petroleum drilling or petroleum conveying operations. In one type the platform is connected directly and in non-yielding fashion to the foundation through a tower shaft, which inhibits any relative movement between the sea bottom and the oil drilling platform. In the second type use is made of a floating construction which allows for inclination in reponse to movements of the surface of the sea under the effect of wind or the like, and in this case use is made of cables, anchors, hawsers or the like to hold the platform in position. Where this construction is used as an oil transfer station or platform only, the oil feed conduit is pivotally connected to the latter.
The first type of above-water platform makes considerable demands on material and is expensive; inter alia this is due to the fact that heavy bending stresses are involved and the fixed end movement between the tower shaft and the foundation has to be compensated.
In the second type an adjustable coupling is provided between the foundation which carries the oil conduit and the oil feed pipe which is supported for example by a steel frame, but the appropriate jointing can only for example be reached by divers. The petroleum conduit -- provided with at least one joint -- can itself incline to the vertical within a certain range. A further disadvantage of this form of oil trans-shipment platform is that the oil conduit lies in the sea water and is directly exposed to acts of sabotage.